Signal processing apparatus, information processing apparatus, signal processing method, data display method, and program

ABSTRACT

In a signal processing apparatus a synchronizer acquires synchronization with the spreading code of an intermediate frequency signal converted from a signal received from a satellite in a global positioning system. A demodulator then demodulates a message contained in the intermediate frequency signal. A measuring unit outputs a primary signal to a predetermined signal line, the primary signal expressing positioning results for the apparatus as measured on the basis of the demodulated message. A secondary signal output unit attaches a predetermined header to a secondary signal and outputs the result to the predetermined signal line, the secondary signal containing at least the intermediate frequency signal, or a signal generated from the intermediate frequency signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal processing apparatus, aninformation processing apparatus, a signal processing method, a datadisplay method, and a program.

2. Description of the Related Art

A variety of electronic devices (such as car navigation equipment,mobile phones, and digital still cameras) are now being equipped withpositioning functions that utilize the Global Positioning System (GPS).Typically, when utilizing GPS in an electronic device, a GPS modulereceives signals from four or more GPS satellites, the device's positionis measured on the basis of the incoming signals, and the user isinformed of the measurement results via the screen of a displayapparatus or similar component. More specifically, the GPS moduledemodulates the incoming signals to acquired orbital data for each GPSsatellite, and then uses a system of equations to derive thethree-dimensional position of the device from the orbital data, timeinformation, and delay times of the incoming signals. Signals arereceived from four or more GPS satellites in order to eliminate theeffects of clock error between the module and the satellites.

Herein, a signal transmitted from a GPS satellite (L1-band, C/A code) isa spread spectrum signal wherein 50 bps data has been spread using Goldcode with a code length of 1023 and a chip rate of 1.023 MHz, andfurthermore wherein the signal has been Binary Phase Shift Keying (BPSK)modulated using a 1575.42 MHz carrier. Consequently, reception of theabove signals from GPS satellites by the GPS module involves spreadingcode, carrier, and data synchronization.

Generally, a GPS module provided in an electronic device firstfrequency-converts the carrier frequency of an incoming signal to anintermediate frequency (IF) of several MHz, and then conductssynchronization and other processing. A typical intermediate frequencymay be 4.092 MHz, 1.023 MHz, or 0 Hz, for example. Normally, the signalstrength of an incoming signal is smaller than the signal strength ofthermal noise, with the S/N ratio falling below 0 dB. However,demodulating the signal is made possible by the process gain of spreadspectrum techniques. In the case of a GPS signal, the process gain withrespect to a 1 bit data length may be (10*log[1.023 MHz/50]), orapproximately 43 dB.

As described above, the market for electronic devices equipped with aGPS module is growing. On the performance side, signal sensitivity isbeing enhanced, and GPS modules having signal sensitivities between −150dBm to −160 dBm are becoming common. However, as GPS modules arebecoming more widespread, the electronic devices equipped with GPSmodules are also increasing in performance. The unwanted electromagneticradiation that emanates from the electronic device as a result becomesnoise, and in a growing number of case, the inherent performance of themodule is not experienced. Noise emanating from the electronic devicecan be caused by various factors, such as internal couplings in thewiring of the electronic device, a clock that interferes spatially, theharmonic components of high-speed signals passing through a data bus orsimilar component, circuit load fluctuations, and power fluctuations bya switching regulator.

If the external noise described above is introduced into the analogcircuits of the GPS module from the electronic device, then signalsensitivity is degraded. Such degradation in signal sensitivity does notpose a problem is the signal strength of the external noise is less thanor on the order of the signal strength of the steady thermal noiseproduced by the GPS module (approximately −111 dBm when computed at 2MHz bandwidth). However, when the signal strength of the external noiseapproaches and exceeds the signal strength of the thermal noise, signalsensitivity degrades to the extent that the level of the steady thermalnoise is exceeded. Furthermore, if the inverse ratio of the incomingsignal versus the sum of the thermal and external noise (hereinafter,S/(N+I)) approaches the process gain, GPS signals might no longer bedetected. Even in the case where the inverse of S/(N+I) is sufficientlysmaller than the process gain, the thermal noise and the GPS signal willbe constrained if the voltage value in the circuit is saturated bystrong external noise, for example. As a result, signal sensitivitydrops sharply. Particularly, the total amplification is 100 dB or morein the case of a typical GPS module, while the resolution ofanalog-to-digital (AD) conversion is 1 or 2 bits. In this case,positioning is basically carried out in a state where the thermal noiseand the GPS signal are saturated to some degree. For this reason, ifexternal noise with a high signal strength is input, then theAD-converted output signal ultimately output by the analog circuit willbe readily saturated.

Consequently, in order to efficiently elicit the performance of a GPSmodule provided in an electronic device, there is a demand forcountermeasures against noise, such as the unwanted radiation emanatingfrom the electronic device. For example, a shielding material orshielding case might be used. As another example, features such as thecircuit board structure, antenna shape, and layout of elements may beoptimized during the design of the electronic device, such that noisepickup by the antenna is minimized. These countermeasures can thereforeaffect the design, cost, and development period of electronic devices.

Consequently, a noise rating apparatus has been proposed, able toquantitatively rate noise with high precision by weighting the levels ofnoise entering a GPS module according to frequency (see, for example,Japanese Patent No. 4060038). Additionally, there have been proposedmethods for detecting anomalous level assumed to noise by using, forexample, the correlation between the C/A code of a non-existentsatellite and an IF signal (see, for example, Japanese Patent No.3949576, and Japanese Unexamined Patent Application Publication Nos.2007-78703 and 2000-249754).

SUMMARY OF THE INVENTION

However, the method disclosed in the above Japanese Patent No. 4060038,for example, may not be effective for optimizing electronic devicedesign, since the scale of the apparatus itself is increased as aresult. Furthermore, noise appearing in signals passing through the GPSmodule is not directly observed in the above method. Meanwhile, in themethods disclosed in Japanese Patent No. 3949576 and Japanese UnexaminedPatent Application Publication Nos. 2007-78703 and 2000-249754, notenough information is provided in order to identify the cause of thenoise, since only the noise level is observed. Generally, directlyobserving external noise entering the GPS module in order to optimizeelectronic device design is difficult for the following reasons.

For example, when using a spectrum analyzer to observe radio frequency(RF) signals directly from the antenna, the GPS signal level is lowerthan that of the thermal noise, as described above, and thus the levelof the external noise to be observed is also low. Thus, a low-noiseamplifier may be placed upstream so that the noise to be observed is notburied in the noise of the spectrum analyzer itself. However, a port orterminal for observation might not be available, such as in the casewhere the antenna is integrated onto the circuit board.

As another example, a spectrum analyzer may be used to observe an IFsignal that has been converted from the carrier frequency of an incomingsignal. Although the signal level is sufficiently amplified at thatpoint, in some cases a port or terminal for acquiring the IF signal isnot provided on the IC of an integrated GPS module. Furthermore, even ifthe IF signal can be acquired via a port, the IF signal is anAD-converted digital signal with a resolution of 2 bits or more, andthus it is difficult to observe the IF signal by simply using a spectrumanalyzer that accepts analog signals.

Moreover, in some cases it is also difficult to draw out leads forobserving signals with a spectrum analyzer from recent GPS modules,which have become increasingly more compact. Also, when testing costsare considered, the use of an expensive spectrum analyzer can itselfbecome a demerit.

In light of the above, it is desirable to provide a signal processingapparatus, an information processing apparatus, a signal processingmethod, a data display method, and a program enabling efficientobservation and analysis of noise appearing in signals passing through aGPS module.

A signal processing apparatus in accordance with an embodiment of thepresent invention includes: a synchronizer configured to acquiresynchronization with the spreading code of an intermediate frequencysignal that is obtained by converting the frequency of a received signalinto a predetermined intermediate frequency, wherein the received signalis received from a satellite in a global positioning system; ademodulator configured to demodulate a message contained in theintermediate frequency signal synchronized by the synchronizer; ameasuring unit configured to output a primary signal to a predeterminedsignal line, wherein the primary signal expresses the results ofmeasuring at least one from among the position, velocity, and time ofthe apparatus as measured on the basis of the message that wasdemodulated by the demodulator; and a secondary signal output unitconfigured to attach a predetermined header to a secondary signal andoutput the result to the predetermined signal line, wherein thesecondary signal contains at least the intermediate frequency signal, ora signal generated from the intermediate frequency signal.

According to such a configuration, a secondary signal containing theintermediate frequency signal (IF signal) and/or a signal generated fromthe IF signal is output from the signal processing apparatus using asignal line for outputting a primary signal expressing the positioningresults. As a result, by connecting an electronic device to this signalline, it becomes possible to acquire information such as the IF signalspectrum and statistical data and directly observe noise conditions,without additional wiring. Herein, such a signal processing apparatusmay be equivalent to, for example, a GPS module 110 in accordance withan embodiment of the present invention, to be hereinafter described.

The secondary signal may also contain a signal expressing a frequencyspectrum generated by applying a Fourier transform to the intermediatefrequency signal.

The secondary signal may also contain a signal expressing data obtainedby statistically analyzing a frequency spectrum generated as a result ofapplying a Fourier transform to the intermediate frequency signal.

The signal processing apparatus may also include a frequency converterconfigured to generate the intermediate frequency signal by convertingthe frequency of a received signal into a predetermined intermediatefrequency, wherein the received signal is received from a satellite in aglobal positioning system.

The secondary signal output unit may also be configured to attach to thesecondary signal a header that contains an ID code for identifying thetype of signal included in the secondary signal.

An information processing apparatus in accordance with anotherembodiment of the present invention includes: a primary signal acquirerconfigured to acquire a primary signal from a predetermined signal line,wherein the primary signal expresses at least one from among theposition, velocity, and time of the apparatus as measured on the basisof an intermediate frequency signal obtained by converting the frequencyof a received signal into an intermediate frequency, and wherein thereceived signal is received from a satellite in a global positioningsystem; a secondary signal acquirer configured to acquire a secondarysignal from the predetermined signal line, wherein the secondary signalcontains at least the intermediate frequency signal, or a signalgenerated from the intermediate frequency signal; and a display unitable to display, on a given screen, data corresponding to the primarysignal acquired by the primary signal acquirer, as well as datacorresponding to the secondary signal acquired by the secondary signalacquirer.

According to such a configuration, not only is a primary signalexpressing positioning results acquired from a signal line, but also asecondary signal containing the IF signal and/or a signal generated fromthe IF signal. Data corresponding to the secondary signal is thendisplayed on a given screen. In so doing, the user is able to directlyobserve noise conditions introduced into the GPS module by referring tothe screen. Herein, such an information processing apparatus may beequivalent to, for example, a display module 160 in accordance with anembodiment of the present invention, to be hereinafter described.

The secondary signal may also contain the intermediate frequency signal,with the apparatus further including a data processor configured togenerate a frequency spectrum by applying a Fourier transform to theintermediate frequency signal. The display unit then displays on-screenthe frequency spectrum generated by the data processor.

The secondary signal may also contain a signal expressing a frequencyspectrum generated by applying a Fourier transform to the intermediatefrequency signal, with the apparatus further including a data processorconfigured to statistically analyze the frequency spectrum contained inthe secondary signal. The display unit then displays on-screen the dataobtained as a result of the analysis by the data processor.

The secondary signal acquirer may also acquire the secondary signal fromamong the signals output to the predetermined signal line by acquiringthe signal whose attached header contains the ID code corresponding tothe secondary signal.

A signal processing method in accordance with another embodiment of thepresent invention includes the steps of: acquiring synchronization withthe spreading code of an intermediate frequency signal that is obtainedby converting the frequency of a received signal into a predeterminedintermediate frequency, wherein the received signal is received from asatellite in a global positioning system; demodulating a messagecontained in the synchronized intermediate frequency signal; outputtinga primary signal to a predetermined signal line, wherein the primarysignal expresses the results of measuring at least one from among theposition, velocity, and time of the apparatus as measured on the basisof the demodulated message; and attaching a predetermined header to asecondary signal and outputting the result to the predetermined signalline, wherein the secondary signal contains at least the intermediatefrequency signal, or a signal generated from the intermediate frequencysignal.

A program in accordance with another embodiment of the present inventioncauses a computer that controls a signal processing apparatus tofunction as: a synchronizer configured to acquire synchronization withthe spreading code of an intermediate frequency signal that is obtainedby converting the frequency of a received signal into a predeterminedintermediate frequency, wherein the received signal is received from asatellite in a global positioning system; a demodulator configured todemodulate a message contained in the intermediate frequency signalsynchronized by the synchronizer; a measuring unit configured to outputa primary signal to a predetermined signal line, wherein the primarysignal expresses the results of measuring at least one from among theposition, velocity, and time of the apparatus as measured on the basisof the message that was demodulated by the demodulator; and a secondarysignal output unit configured to attach a predetermined header to asecondary signal and output the result to the predetermined signal line,wherein the secondary signal contains at least the intermediatefrequency signal, or a signal generated from the intermediate frequencysignal.

A data display method in accordance with another embodiment of thepresent invention is executed using an information processing apparatusable to display data on a given screen, the method including the stepsof: acquiring a primary signal from a predetermined signal line, whereinthe primary signal expresses at least one from among the position,velocity, and time of the apparatus as measured on the basis of anintermediate frequency signal obtained by converting the frequency of areceived signal into an intermediate frequency, and wherein the receivedsignal is received from a satellite in a global positioning system;acquiring a secondary signal from the predetermined signal line, whereinthe secondary signal contains at least the intermediate frequencysignal, or a signal generated from the intermediate frequency signal;and displaying, on the given screen, data corresponding to the primarysignal, as well as data corresponding to the secondary signal.

A program in accordance with another embodiment of the present inventionis executed by a computer that controls an information processingapparatus able to display data on a given screen. The program causes thecomputer to function as: a primary signal acquirer configured to acquirea primary signal from a predetermined signal line, wherein the primarysignal expresses at least one from among the position, velocity, andtime of the apparatus as measured on the basis of an intermediatefrequency signal obtained by converting the frequency of a receivedsignal into an intermediate frequency, and wherein the received signalis received from a satellite in a global positioning system; a secondarysignal acquirer configured to acquire a secondary signal from thepredetermined signal line, wherein the secondary signal contains atleast the intermediate frequency signal, or a signal generated from theintermediate frequency signal; and a display unit able to display, onthe given screen, data corresponding to the primary signal acquired bythe primary signal acquirer, as well as data corresponding to thesecondary signal acquired by the secondary signal acquirer.

As described above, according to a signal processing apparatus,information processing apparatus, signal processing method, data displaymethod, and program in accordance with embodiments of the presentinvention, it becomes possible to efficiently observe and analyze noiseappearing in signals passing through a GPS module.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of a GPS modulerelated to the present invention;

FIG. 2 is a block diagram illustrating an exemplary detailedconfiguration of the synchronizer shown in FIG. 1;

FIG. 3 is a block diagram illustrating another exemplary detailedconfiguration of the synchronizer shown in FIG. 1;

FIG. 4 is an explanatory diagram illustrating an exemplary correlationsignal peak output from a digital matched filter;

FIG. 5 is a diagram for explaining the spectrum of an IF signal beforeAD conversion;

FIG. 6 is a diagram for explaining the spectrum of an IF signal after ADconversion;

FIG. 7 is a schematic diagram illustrating an exemplary configuration ofa GPS system in accordance with an embodiment of the present invention;

FIG. 8 is a schematic diagram illustrating another exemplaryconfiguration of a GPS system in accordance with an embodiment of thepresent invention;

FIG. 9 is a block diagram illustrating an exemplary logicalconfiguration of a GPS module in accordance with an embodiment of thepresent invention;

FIG. 10 is a diagram for explaining the processing patterns of asecondary signal output unit in accordance with an embodiment of thepresent invention;

FIG. 11 is an explanatory diagram illustrating an exemplary format of asecondary signal in accordance with an embodiment of the presentinvention;

FIG. 12 is an explanatory diagram illustrating exemplary data in asecondary signal in accordance with an embodiment of the presentinvention;

FIG. 13 is a block diagram illustrating an exemplary logicalconfiguration of a display module in accordance with an embodiment ofthe present invention;

FIG. 14 is an explanatory diagram illustrating exemplary data displayedon a screen in accordance with an embodiment of the present invention;and

FIG. 15 is a schematic diagram illustrating an exemplary configurationof a system for testing an antenna or frequency converter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail and with reference to the accompanying drawings. Inthe specification and drawings herein, component elements havingessentially the same functional configurations are given identicalreference numbers, and repeated description thereof is omitted.

The preferred embodiments will be described in the following order.

1. Description of GPS module related to the present invention

2. Description of embodiment

-   -   2-1. System overview    -   2-2. Exemplary configuration of GPS module    -   2-3. Exemplary secondary signal format    -   2-4. Exemplary configuration of display module

3. Description of modification

1. Description of GPS Module Related to the Present Invention

FIG. 1 is a block diagram illustrating the hardware configuration of aGPS module 10 related to the present invention.

With reference to FIG. 1, the GPS module 10 is provided with an antenna12, a frequency converter 20, a synchronizer 40, a demodulator 50, acentral processing unit (CPU) 60, a realtime clock (RTC) 64, a timer 68,memory 70, a crystal oscillator (XO) 72, a temperature-compensatedcrystal oscillator (TCXO) 74, and a multiplier/divider 76.

Oscillation of the XO 72 produces a signal D1 having a predeterminedfrequency (such as approximately 32.768 kHz, for example). The producedsignal D1 is supplied to the RTC 64. Oscillation of the TCXO 74 producesa signal D2 having a frequency different from that of the XO 72 (such asapproximately 16.368 MHz, for example). The produced signal D2 issupplied to both the multiplier/divider 76 and a frequency synthesizer28.

On the basis of instructions from the CPU 60, the multiplier/divider 76multiplies, divides, or both multiplies and divides the signal D2supplied from the TCXO 74. Subsequently, the multiplier/divider 76supplies the resulting signal D4 to the frequency synthesizer 28 of thefrequency converter 20, an ADC 36, the CPU 60, the timer 68, the memory70, the synchronizer 40, and the demodulator 50.

The antenna 12 receives a wireless signal containing a navigationmessage or other information that was transmitted from a GlobalPositioning System (GPS) satellite. (For example, the wireless signalmay be an RF spread spectrum signal on a 1575.42 MHz carrier frequency.)The antenna 12 converts the received wireless signal to an electricalsignal D5, and then supplies the result to the frequency converter 20.

The frequency converter 20 is provided with a low noise amplifier (LNA)22, a band pass filter 24, an amplifier 26, the frequency synthesizer28, a multiplier 30, an amplifier 32, a low pass filter (LPF) 34, and ananalog-to-digital converter (ADC) 36. As described hereinafter, in orderto simplify digital signal processing, the frequency converter 20 takesthe signal D5 having the high frequency of 1575.42 MHz that was receivedby the antenna 12, and downconverts to a signal D14 having a frequencyof approximately 1.023 MHz, for example.

The LNA 22 amplifies the signal D5 supplied from the antenna 12, andsupplies the result to the BPF 24. The BPF 24 is made up of a surfaceacoustic wave (SAW) filter, and extracts only a specific frequencycomponent from among the frequency components in the amplified signal D6from the LNA 22. The extracted frequency components are then supplied tothe amplifier 26. The amplifier 26 amplifies the signal D7 containingthe frequency component that was extracted by the BPF 24 (i.e., thefrequency F_(RF)), and supplies the result to the multiplier 30.

On the basis of instructions D9 from the CPU 60, the frequencysynthesizer 28 uses the signal D2 supplied from the TCXO 74 to generatea signal D10 having a frequency F_(LO). Subsequently, the frequencysynthesizer 28 supplies the generated signal D10 having the frequencyF_(LO) to the multiplier 30.

The multiplier 30 multiplies the signal D8, having the frequency F_(RF)and supplied from the amplifier 26, by the signal D10, having thefrequency F_(LO) and supplied from the frequency synthesizer 28. Inother words, the multiplier 30 downconverts the high-frequency signal toan intermediate frequency (IF) signal D11 (such as an intermediatefrequency of approximately 1.023 MHz, for example).

The amplifier 32 amplifies the downconverted IF signal D11 from themultiplier 30, and supplies the result to the LPF 34.

The LPF 34 extracts the low-frequency component from among the frequencycomponents of the amplified IF signal D12 from the multiplier 30, andsupplies a signal D13 having the extracted low-frequency component tothe ADC 36. Herein, FIG. 1 shows the LPF 34 being placed between theamplifier 32 and the ADC 36 by way of example, but a BPF may also beplaced between the amplifier 32 and the ADC 36.

The ADC 36 converts the analog IF signal D13 supplied from the LPF 34into a digital format by means of sampling, and then supplies theconverted digital IF signal D14 to the synchronizer 40 and thedemodulator 50 one bit at a time.

On the basis of control by the CPU 60, the synchronizer 40 uses thesignal D3 supplied from the multiplier/divider 76 to acquire sync withpseudo-random noise (PRN) in the IF signal D14 supplied from the ADC 36.Additionally, the synchronizer 40 detects the carrier frequency of theIF signal D14. Subsequently, the synchronizer 40 supplies informationsuch as the phase of the PRN and the carrier frequency of the IF signalD14 to the demodulator 50 and the CPU 60.

On the basis of control by the CPU 60, the demodulator 50 uses thesignal D3 supplied from the multiplier/divider 76 to maintain sync withthe PRN and the carrier of the IF signal D14 supplied from the ADC 36.More specifically, the demodulator 50 operates by taking the PRN phaseand carrier frequency of the IF signal D14 that were supplied from thesynchronizer 40 as initial values. The demodulator 50 then demodulatesthe navigation message contained in the IF signal D14 supplied from theADC 36, and supplies the demodulated navigation message, as well as boththe high-precision PRN phase and carrier frequency, to the CPU 60.

On the basis of the navigation message, PRN phase, and carrier frequencysupplied from the demodulator 50, the CPU 60 computes the positions andvelocities of respective GPS satellites, and calculates the position ofthe GPS module 10. The CPU 60 may also correct the time information ofthe RTC 64 on the basis of the navigation message. The CPU 60 may alsobe connected to control, I/O, option, and similar ports, and may executevarious other types of control processes.

Using the signal D1 having a predetermined frequency and supplied fromthe XO 72, the RTC 64 measures the time. The time as measured by the RTC64 may be corrected by the CPU 60 as appropriate.

Using the signal D4 supplied from the multiplier/divider 76, the timer68 counts time. Such a timer 68 is referenced in particular situations,such as when determining the start timing for various control processesexecuted by the CPU 60. For example, the CPU 60 may reference the timer68 when determining the timing for initiating a PRN generator in thedemodulator 50 on the basis of the PRN phase acquired by thesynchronizer 40.

The memory 70 may be realized by means of random access memory (RAM) andread-only memory (ROM). The memory 70 functions as work space for theCPU 60, as a program storage unit, and as a navigation message storageunit, for example. In the memory 70, RAM is used as a work area when theCPU 60 or similar component executes various processes. Additionally,RAM may also be used in order to buffer various input data, to store theephemeris and almanac data included in the GPS satellite orbitalinformation obtained by the demodulator 50, as well to store bothintermediate data generated partway during computational processes andcomputational results data. Meanwhile, in the memory 70, ROM is used asa means to store various programs, static data, and similar information.Furthermore, in some cases non-volatile memory may be used in the memory70 as a means to store information while the GPS module 10 is poweredoff. Such information may include the ephemeris and almanac dataincluded in the GPS satellite information, position information frompositioning results, and TCXO 74 error values.

Herein, the respective blocks of the GPS module 10 shown in FIG. 1(excluding the XO 72, TCXO 74, antenna 12, and BPF 24) can also bemounted on an integrated circuit made up of a single chip.

In order to quickly achieve sync acquisition of the spreading code, thesynchronizer 40 herein may use a matched filter, for example. Morespecifically, the synchronizer 40 may also use the transversal filter 40a shown by way of example in FIG. 2 as a matched filter. Alternatively,the synchronizer 40 may also use the digital matched filter 40 b thatutilizes the fast Fourier transform (FFT) shown by way of example inFIG. 3 as a matched filter.

For example, referring to FIG. 3, the digital matched filter 40 bincludes memory 41, an FFT unit 42, memory 43, a spreading codegenerator 44, an FFT unit 45, memory 46, a multiplier 47, an inversefast Fourier transform (IFFT) unit 48, and a peak detector 49.

The memory 41 buffers the sampled IF signal from the ADC 36 of thefrequency converter 20. The FFT unit 42 reads out the IF signal bufferedby the memory 41, and applies the fast Fourier transform thereto. Thememory 43 buffers the frequency-domain signal obtained as a result ofconverting the time-domain IF signal using the fast Fourier transform inthe FFT unit 42.

Meanwhile, the spreading code generator 44 generates spreading codeidentical to the spreading code in the RF signal from the GPS satellite.The FFT unit 45 applies the fast Fourier transform to the spreading codegenerated by the spreading code generator 44. The memory 46 buffers thefrequency-domain signal obtained as a result of converting thetime-domain spreading code using the fast Fourier transform in the FFTunit 45.

The multiplier 47 multiplies the frequency-domain signal buffered in thememory 43 by the frequency-domain spreading code buffered in the memory46. The IFFT unit 48 applies the inverse fast Fourier transform to themultiplied frequency-domain signal output from the multiplier 47. In sodoing, a correlation signal in the time domain is acquired between thespreading code in the RF signal from the GPS satellite, and thespreading code generated by the spreading code generator 44.Subsequently, the peak detector 49 detects peaks in the correlationsignal output from the IFFT unit 48.

Such a digital matched filter 40 b may also be realized in software thatuses a digital signal processor (DSP) to execute the processing of theFFT units 42 and 45, the spreading code generator 44, the multiplier 47,the IFFT unit 48, and the peak detector 49, respectively.

FIG. 4 is an explanatory diagram illustrating an exemplary correlationsignal peak acquired by the digital matched filter 40 a or 40 bdescribed above. Referring to FIG. 4, a peak P1 where the correlationlevel spikes is detected in a single period of the output waveform ofthe correlation signal. The position of such a peak P1 on the time axiscorresponds to the beginning of the spreading code. In other words, bydetecting peaks like the above peak P1, the synchronizer 40 is able todetect synchronization with incoming signals received from GPSsatellites (i.e., detect the phase of the spreading code).

FIGS. 5 and 6 are diagrams for explaining the spectra of an IF signalbefore and after AD conversion, in the case where external noise isintroduced into the GPS module 10.

The upper part of FIG. 5 illustrates the spectrum of an IF signal beforeAD conversion by the ADC 36, in the case where strong, mono-frequencyexternal noise is introduced into the GPS module 10. The external noisemay be caused by the clock or similar component of a personal computer(PC), for example. Herein, the spectrum is shown such that the sign ofthe frequency is inverted about the center of the frequency (i.e.,horizontal) axis. In FIG. 5, strong, spiking noise having a frequencyslightly less than 6 MHz is observed. This noise is the mono-frequencyexternal noise caused by a clock or similar component of a PC.Additionally, in the frequency from approximately 1 MHz to approximately7 MHz, strong, uniform noise is observed. This noise corresponds to thethermal noise after passing through the BPF. Meanwhile, the lower partof FIG. 5 illustrates the results of using a predetermined spreadingcode to de-spread an IF signal having a spectrum like that shown in theupper part of FIG. 5. In the lower part of FIG. 5, a peak P2 is detectedin the central portion of the phase range of the 1023-bit spreadingcode. This peak P2 expresses the phase of the GPS signal acquired byde-spreading. Consequently, FIG. 5 demonstrates that if the IF signalhas not yet been AD-converted, then GPS signal sync can be acquiredwithout saturating the signal.

In contrast, the upper part of FIG. 6 illustrates the spectrum of an IFsignal after AD conversion by the ADC 36, in the case where the strong,mono-frequency external noise described above is introduced into the GPSmodule 10. Herein, the resolution of the ADC 36 is taken to be 2 bits.In FIG. 6, spiking noise is observed at a plurality of frequencies, dueto the output signal from the ADC 36 being saturated by external noise.Furthermore, in the de-spreading results shown in lower part of FIG. 6,the GPS signal is suppressed, and as a result, the phase of the GPSsignal does not appear as a peak, and thus sync is not acquired for theGPS signal. In other words, FIG. 6 demonstrates that even if the IFsignal is not saturated while in analog and the process gain of thede-spreading process is sufficiently higher than the inverse of S/(N+I),the signal might still be saturated in digital after AD conversion with2-bit resolution, and the GPS signal might not be detected.

In conditions where such external noise is present, the inherentperformance of the GPS module is not expressed. Consequently, whendesigning, manufacturing, or testing electronic devices provided withGPS modules, there is demand to observe and develop countermeasures forthe types of effects exerted on the GPS module by noise produced by theelectronic device. However, due to the reasons given earlier, directlyobservation of external noise introduced into the GPS module is noteasy. Given the above, the configuration in accordance with anembodiment of the present invention to be described in the followingsection enables observation and analysis of external noise introducedinto a GPS module, without involving additional wiring or specializedmeasuring equipment.

2. Description of Embodiment 2-1. System Overview

FIG. 7 illustrates an exemplary schematic configuration of a GPS systemin accordance with an embodiment of the present invention. In FIG. 7, aGPS system 100 a is shown to include an antenna 102, a signal line 104,a GPS module 110, and a display module 160.

Similarly to the antenna 12 shown in FIG. 1, the antenna 102 receives awireless signal containing a navigation message or other informationthat was transmitted from a GPS satellite, and supplies the receivedsignal to the GPS module 110.

The signal line 104 connects the GPS module 110 to the display module160. Typically, the signal line 104 is used for serial transmission ofsignals between the GPS module 110 and the display module 160.

In response to commands input from the display module 160 via the signalline 104, the GPS module 110 conducts various processes, such asconverting the frequency of an incoming signal supplied from the antenna102, acquiring sync with an IF signal, demodulating a navigationmessage, and executing positioning processing, for example.Subsequently, the GPS module 110 outputs to the signal line 104 aprimary signal expressing information such as the results of thepositioning processing. Additionally, in the present embodiment, the GPSmodule 110 outputs to the signal line 104 a secondary signal used toobserve and analyze noise introduced into the GPS module 110, as furtherdescribed hereinafter. Herein, the format of the primary signal andsecondary signal output by the GPS module 110 may follow a standardspecification such as National Marine Electronics Association (NMEA)0183, or an independently-defined format.

Via the signal line 104, the display module 160 outputs to the GPSmodule 110 commands containing various instructions, such as startingthe positioning process, and starting or resetting the secondary signaloutput process, for example. In addition, via the signal line 104, thedisplay module 160 acquires the primary signal and secondary signaldescribed earlier that are output from the GPS module 110. Subsequently,the display module 160 displays information on a given screen providedin the display module 160. The information may be, for example, theresults of the positioning process as expressed by the primary signal,the content of the secondary signal, or similar information.

FIG. 8 illustrates another exemplary schematic configuration of a GPSsystem in accordance with an embodiment of the present invention. InFIG. 8, a GPS system 100 b is shown to include an antenna 102, signallines 104 a and 104 b, a connecting line 106, a GPS module 110, and adisplay module 160.

In the GPS system 100 b, the signal line between the GPS module 110 andthe display module 160 is split into the signal lines 104 a and 104 b,with the connecting line 106 connecting the two signal lines. Theconnecting line 106 may be, for example, a cable based on a serialcommunication standard such as RS-232C, USB, or Bluetooth™. In thiscase, conversion ports adhering to one of the above serial communicationstandards are provided between the connecting line 106 and therespective signal lines 104 a and 104 b.

The configuration of the GPS system 100 a shown in FIG. 7 is applicableto an electronic device wherein the GPS module 110 is built onto thecircuit board in advance, such as a mobile phone handset, car navigationequipment, or digital still camera, for example. In this case, thedisplay module 160 is implemented as a host module of the electronicdevice. In contrast, the configuration of the GPS system 100 b shown inFIG. 8 is applicable to an electronic device wherein the GPS module 110is externally attached or linked, for example. In this case, the displaymodule 160 is implemented as the principal unit of the electronicdevice, such as a mobile personal computer (PC) or personal digitalassistant (PDA).

More specific configurations of the GPS module 110 and the displaymodule 160 described above will now be described.

2-2. Exemplary Configuration of GPS Module

FIG. 9 is a block diagram illustrating in detail the logicalconfiguration of a GPS module 110 in accordance with the presentembodiment. In FIG. 9, the GPS module 110 is primarily provided with afrequency converter 120, a synchronizer 130, a demodulator 132, ameasuring unit 140, and a secondary signal output unit 150.

Similarly to the frequency converter 20 shown in FIG. 1, the frequencyconverter 120 amplifies a signal received from a GPS satellite via theantenna 102, and generates an IF signal by converting the frequency ofthe incoming signal to a predetermined intermediate frequency. Inaddition, the frequency converter 120 uses sampling to convert theanalog IF signal into a digital signal. Subsequently, the frequencyconverter 120 supplies the converted digital IF signal to thesynchronizer 130, demodulator 132, and secondary signal output unit 150.

Similarly to the synchronizer 40 shown in FIG. 1, the synchronizer 130using a predetermined spreading code for sync acquisition with the IFsignal supplied from the frequency converter 120. In addition, thesynchronizer 130 detects the carrier frequency of the IF signal.Subsequently, the synchronizer 130 supplies the acquired phase of thespreading code and the carrier frequency of the IF signal to thedemodulator 132 and the measuring unit 140. The synchronizer 130 mayalso be configured to use the transversal filter 40 a shown by way ofexample in FIG. 2. Alternatively, the synchronizer 130 may be configuredto use the digital matched filter 40 b shown by way of example in FIG.3. Furthermore, the synchronizer 130 may also output to the secondarysignal output unit 150 the frequency spectrum obtained by applying afast Fourier transform to the IF signal, as described later.

Similarly to the demodulator 50 shown in FIG. 1, the demodulator 132uses the spreading code phase and carrier frequency input from thesynchronizer 130 as a basis for demodulating the navigation messagecontained in the IF signal and detecting the high-precision PRN phaseand carrier frequency. Subsequently, the demodulator 132 supplies thedemodulated navigation message, high-precision PRN phase, and carrierfrequency to the measuring unit 140.

On the basis of the navigation message, PRN phase, and carrier frequencysupplied from the demodulator 132, the measuring unit 140 uses the CPU60 shown in FIG. 1 to compute the positions and velocities of respectiveGPS satellites, and measures at least one from among the position,velocity, and time of the GPS module 110. Subsequently, the measuringunit 140 outputs a primary signal expressing the measurement results tothe signal line 104.

The secondary signal output unit 150 attaches a predetermined header toa secondary signal, and outputs the secondary signal to the signal line104. The secondary signal herein contains at least the IF signalsupplied from the frequency converter 120, or a signal generated as aresult of processing the IF signal in a given way.

FIG. 10 is a diagram for explaining processing patterns in the secondarysignal output unit 150. In FIG. 10, five processing patterns fromPattern 1 to Pattern 5 executed by the secondary signal output unit 150are shown by way of example. Additionally, for each processing pattern,there is shown the supplier of the input signal to the secondary signaloutput unit 150, the input signal type, the type of processing executed,and the output signal type.

First, in the case of Pattern 1, an IF signal is supplied to thesecondary signal output unit 150 from the frequency converter 120. Oncethe IF signal is supplied, the secondary signal output unit 150 extractsa predetermined, finite-length signal sequence from the continuous IFsignal. Next, the secondary signal output unit 150 generates a secondarysignal by attaching a header to the finite-length signal sequence of theIF signal, wherein the header contains an ID code indicating that thesignal type is an IF signal. Besides the ID code, the header attached tothe secondary signal may also contain arbitrary information such as thedata length, for example. Subsequently, the secondary signal output unit150 outputs the generated secondary signal to the signal line 104.

In the case of Pattern 2, an IF signal is supplied to the secondarysignal output unit 150 from the frequency converter 120, similarly toPattern 1. Once the IF signal is supplied, the secondary signal outputunit 150 applies a fast Fourier transform to a finite-length signalsequence extracted from the continuous IF signal. Next, the secondarysignal output unit 150 generates a secondary signal by attaching aheader to the frequency spectrum obtained as a result of the fastFourier transform, wherein the header contains an ID code indicatingthat the signal type is a frequency spectrum for an IF signal.Subsequently, the secondary signal output unit 150 outputs the generatedsecondary signal to the signal line 104.

In the case of Pattern 3, an IF signal is supplied to the secondarysignal output unit 150 from the frequency converter 120, similarly toPatterns 1 and 2. Once the IF signal is supplied, the secondary signaloutput unit 150 first applies a fast Fourier transform to afinite-length signal sequence extracted from the continuous IF signal.Next, the secondary signal output unit 150 performs statistical analysison the frequency spectrum obtained as a result of the fast Fouriertransform. More specifically, the secondary signal output unit 150 maycompute information such as several dominant frequencies expressing highnoise levels in the frequency spectrum, the ratio of the measured powerversus the power in an ideal state measured in advance, and a timeaverage or distribution of the noise levels. The secondary signal outputunit 150 then generates a secondary signal by attaching a header to thestatistical data computed by the statistical analysis, wherein theheader contains an ID code indicating the data type. Subsequently, thesecondary signal output unit 150 outputs the generated secondary signalto the signal line 104.

In the case of Pattern 4, the frequency spectrum of an IF signal issupplied to the secondary signal output unit 150 from the synchronizer130. The frequency spectrum supplied at this point may be, for example,the frequency spectrum resulting from the FFT being applied to the IFsignal by the FFT unit 42 of the digital matched filter 40 b, in thecase where the synchronizer 130 is configured to use the digital matchedfilter 40 b shown by way of example in FIG. 3. Once the frequencyspectrum is supplied, the secondary signal output unit 150 generates asecondary signal by attaching a header to the supplied frequencyspectrum, wherein the header contains an ID code indicating that thesignal type is a frequency spectrum. Subsequently, the secondary signaloutput unit 150 outputs the generated secondary signal to the signalline 104.

In the case of Pattern 5, the frequency spectrum of an IF signal issupplied to the secondary signal output unit 150 from the synchronizer130, similarly to Pattern 4. Once the frequency spectrum is supplied,the secondary signal output unit 150 performs statistical analysis onthe supplied frequency spectrum. The statistical analysis processingexecuted at this point may be similar to that of the above Pattern 3.The secondary signal output unit 150 then generates a secondary signalby attaching a header to the statistical data obtained as a result ofthe statistical analysis, wherein the header contains an ID codeindicating the data type. Subsequently, the secondary signal output unit150 outputs the generated secondary signal to the signal line 104.

The secondary signal output unit 150 executes processing for one of theabove five processing patterns in response to commands input from thedisplay module 160, for example. Additionally, the secondary signaloutput unit 150 may also execute processing for a plurality of the fiveprocessing patterns, and generate a secondary signal jointly containingthe results from each process.

Herein, the signal line to which the secondary signal output unit 150outputs the secondary signal is the same signal line 104 to which themeasuring unit 140 outputs the primary signal. Thus, in order to avoidcollision with the primary signal from the measuring unit 140, thesecondary signal output unit 150 outputs the secondary signal at atiming when the primary signal is not being output from the measuringunit 140. For example, assume that the frequency spectrum of the IFsignal is included in the secondary signal, as in the above Patterns 2and 4. Assuming that there are 1024 FFT points, and that the bit lengthfor the absolute value of each frequency component is 8 bits, then thedata length of the frequency spectrum of the IF signal becomes 8 kboverall. Consequently, if the secondary signal output rate is assumed tobe once every several seconds, for example, then it is possible totransfer secondary signals using a signal line shared with the primarysignals, even when using the low-speed serial transmission techniquesshown in FIGS. 7 and 8.

Herein, the respective processing performed by the secondary signaloutput unit 150 may also be physically executed using a CPU shared withthe measuring unit 140 (such as the CPU 60 of the GPS module 10 shown inFIG. 1, for example). Alternatively, the respective processing performedby the secondary signal output unit 150 may also be physically executedusing the DSP used by the synchronizer 130 or the demodulator 132, oradditionally provided hardware. In the case of using a general-purposeCPU to execute fast Fourier transforms, statistical analysis, and otherprocessing performed by the secondary signal output unit 150,computations may take more time as compared to execution using a DSP orspecial-purpose hardware. However, if the above processing is taken touse the CPU sporadically or at low frequency during the idle timesbetween the positioning computations performed by the measuring unit140, then the secondary signal output unit 150 can output secondarysignals without stressing CPU resources.

2-3. Exemplary Secondary Signal Format

FIG. 11 is an explanatory diagram illustrating an exemplary format of asecondary signal output by the secondary signal output unit 150 inaccordance with the present embodiment.

In FIG. 11, the secondary signal format includes a header 152, a datafield 154, and a trailer 156. The header 152 contains the ID code foridentifying the type of signal included in the secondary signal, as wellas predetermined data attributes. The data attributes correspond toinformation such as the data length of the entire secondary signal or ofthe data portion 154, for example. The data field 154 contains theinformation shown in the output signal column of FIG. 10, such as afinite-length IF signal, the frequency spectrum of the IF signal, and/orstatistical data expressing the results of analyzing the frequencyspectrum, for example. The trailer 156 may contain the ID code found inthe header 152, as well as an exit code indicating the end of thesecondary signal. Herein, FIG. 11 shows a two-dimensional format foldedat fixed byte intervals, but it should be appreciated that in practice,a secondary signal is normally a one-dimensional bit sequence.

FIG. 12 is an explanatory diagram illustrating exemplary secondarysignal data. By way of example, FIG. 12 shows the case where thefrequency spectrum of an IF signal is included in the secondary signalby using the user-defined extension format stipulated in NMEA 0183.

In FIG. 12, the header 152 of the secondary signal contains an ID code152 a, for example. In the text string “$PCMF” of the ID code 152 a, thesymbol “$” is the format start symbol. The 1-byte “P” following thesymbol “$” indicates that the secondary signal is in a user-definedformat. The following 2-byte “CM” is a predetermined company code. Thefollowing 1-byte “F” indicates that the data field 154 of the currentsecondary signal contains the frequency spectrum of the IF signal. Inother words, by varying the character in the,fifth byte of the ID code152 a according to the type of signal included in the secondary signal,for example, an ID code able to identify the signal type can be formed.Meanwhile, NMEA 0183 stipulates that the ID code of a primary signalexpressing the position data output from the measuring unit 140 shouldstart with “$GSV”, for example. Consequently, the display module 160 tobe hereinafter described that receives the secondary signal is able todistinguish between the primary signal and the secondary signal byreferencing such ID codes.

The frequency spectrum 154 a of the IF signal starts on the second lineof the data field 154 of the secondary signal shown in FIG. 12. Herein,the frequency spectrum 154 a is a hexadecimal image with 16 points perline and 16 lines, for a total of 256 points. The secondary signaloutput unit 150 generates such a secondary signal, for example, andoutputs the signal to the signal line 104.

Although the secondary signal format is herein described in accordancewith NMEA 0183, it should be appreciated that the secondary signalformat is not limited to such an example. For example, by using anindependently-defined secondary signal format, it is possible to freelyinclude arbitrary bit sequences in the secondary signal and efficientlytransmit signals.

2-4. Exemplary Configuration of Display Module

FIG. 13 is a block diagram illustrating in detail the logicalconfiguration of a display module 160 in accordance with the presentembodiment. In FIG. 13, the display module 160 is primarily providedwith a primary signal acquirer 170, a secondary signal acquirer 172, adata processor 174, a controller 180, and a display unit 190.

From the signal line 104, the primary signal acquirer 170 acquires aprimary signal expressing at least one from among the position,velocity, and time that were measured on the basis of the IF signal inthe measuring unit 140 of the GPS module 110. More specifically, theprimary signal acquirer 170 may acquire the primary signal from amongthe signals received via the signal line 104 by acquiring the signalstarting with the ID code corresponding to the primary signal, forexample. The ID code corresponding to the primary signal may be an IDcode starting with “$GSV” as stipulated in NMEA 0183 described above,for example. Subsequently, the primary signal acquirer 170 outputs theacquired primary signal to the data processor 174.

From the signal line 104, the secondary signal acquirer 172 acquires thesecondary signal generated by the secondary signal output unit 150 ofthe GPS module 110, the secondary signal herein containing informationsuch as the IF signal, or a frequency spectrum or statistical datagenerated from the IF signal. More specifically, the secondary signalacquirer 172 may acquire the secondary signal from among the signalsreceived via the signal line 104 by acquiring the signal starting withthe ID code corresponding to the secondary signal, for example. The IDcode corresponding to the secondary signal may be an ID code like thatshown by way of example in FIG. 12, for example. Subsequently, thesecondary signal acquirer 172 outputs the acquired secondary signal tothe data processor 174.

The data processor 174 extracts data to be displayed on a given screenfrom the primary signal or secondary signal, for example, and alsoprocesses the data as appropriate. Assume, for example, that afinite-length IF signal is included in a secondary signal output fromthe secondary signal output unit 150 of the GPS module 110 in accordancewith Pattern 1 shown in FIG. 10. In this case, the data processor 174first extracts the finite-length IF signal from the secondary signal.The data processor 174 may then apply the fast Fourier transform to theextracted IF signal to generate a frequency spectrum, and maystatistically analyze the frequency spectrum to compute statisticaldata, as appropriate. Typically, statistical data corresponds toinformation such as several dominant frequencies expressing high noiselevels in the frequency spectrum, the ratio of the measured power versusthe power in an ideal state measured in advance, and a time average ordistribution of the noise levels.

As another example, assume that the frequency spectrum of the IF signalis included in a secondary signal output from the secondary signaloutput unit 150 in accordance with Pattern 2 or 4 shown in FIG. 10. Inthis case, the data processor 174 first extracts the frequency spectrumof the IF signal from the secondary signal. The data processor 174 thenstatistically analyzes the extracted frequency spectrum to computestatistical data, as appropriate.

As another example, assume that statistical data resulting fromstatistical analysis performed on the frequency spectrum of the IFsignal is included in a secondary signal output from the secondarysignal output unit 150 in accordance with Pattern 3 or 5 shown in FIG.10. In this case, the data processor 174 extracts the statistical datafrom the secondary signal.

Subsequently, the data processor 174 outputs to the controller 180 thedata that was extracted or generated from the primary signal orsecondary signal. Herein, if the display module 160 is a PC or similardevice having a relatively high-performance CPU, for example, then it ispreferable for processes such as fast Fourier transforms and statisticalanalysis to be conducted by the data processor 174 of the display module160. In contrast, if the display module 160 is a small, portable devicehaving only a relatively low-performance CPU, then it is preferable forprocesses such as fast Fourier transforms and statistical analysis to beconducted in the GPS module 110.

The controller 180 sends predetermined commands to the GPS module 110via the signal line 104, for example, and controls the operation of theGPS module 110. In addition, when data corresponding to a primary signalor secondary signal received from the GPS module 110 is input from thedata processor 174, the controller 180 may output the data to thedisplay unit 190 and cause the data to be displayed on a given screen,for example. Besides the above, the controller 180 also controls thegeneral functionality of the display module 160.

The primary signal acquirer 170, secondary signal acquirer 172, dataprocessor 174, and controller 180 described above are also typicallyrealizable as software executed by the host CPU of an electronic device,such as a mobile phone handset, car navigation equipment, or a PC. Insuch cases, a program constituting the software is stored in advance ona hard disk or in semiconductor memory such as ROM that is accessible bythe display module 160.

The display unit 190 displays various data input from the controller 180on a given screen provided in the electronic device housing the displaymodule 160, for example. FIG. 14 is an explanatory diagram illustratingexemplary data displayed on a screen by the display unit 190.

In FIG. 14, a GPS monitor screen 192 is shown as one example of datathat may be displayed by the display unit 190. The GPS monitor screen192 includes a measurement results display area 194, a satellite datadisplay area 195, a frequency spectrum display area 197, a statisticaldata display area 198, and a command button area 199.

The measurement results display area 194 is an area displaying dataexpressed by the primary signal, such as the position and velocitycomputed as a result of the measuring process conducted by the measuringunit 140 of the GPS module 110. In the example shown in FIG. 14, themeasurement results display area 194 shows current latitude (Lat.),longitude (Lon.), altitude (Alt.), and velocity (Vel.) values for theGPS module 110. The satellite data display area 195 displays optionaldata that can be included in the primary signal. In FIG. 14, the signalstrength (Lv.) and Doppler shift frequency (Freq.) of each GPS satelliteis displayed according to satellite ID.

The frequency spectrum display area 197 is an area for displaying thefrequency spectrum of the IF signal. The frequency spectrum display area197 may, for example, display a graph of a frequency spectrum extractedfrom the secondary signal, or a frequency spectrum generated by the dataprocessor 174 of the display module 160 from an IF signal included inthe secondary signal. The statistical data display area 198 is an areafor displaying statistical data obtained by statistically analyzing thefrequency spectrum of the IF signal. In the example shown in FIG. 14,the statistical data display area 198 shows the values of the top threefrequencies exhibiting high noise levels in the frequency spectrum (PeakFreq. 1-3), as well as the ratio of the measured power versus the powerin the ideal state (Power Ratio). Meanwhile, in the command button area199, there are arranged command buttons for transmitting commands to theGPS module 110. The commands herein are for changing the number of FFTpoints (256 bit, 512 bit, 1024 bit) when generating the frequencyspectrum.

The display unit 190 thus displays various data corresponding to theprimary signal or secondary signal input from the controller 180on-screen via such a GPS monitor screen 192, for example.

The foregoing thus describes the detailed configuration of a GPS module110 and a display module 160 in accordance with an embodiment of thepresent invention, and with reference to FIGS. 9 to 14. According tosuch a configuration, noise introduced into the GPS module 110 can bedirectly observed using the screen of the display module 160, whichdisplays the noise spectrum and statistical data for the spectrum.Consequently, it becomes possible to conduct design optimization testingfor achieving the inherent performance of the GPS module 110 whenprovided in an electronic device, the testing being conducted on thebasis of direct and quantitative data, and not trial-and-error methodslike those of the related art.

Furthermore, the foregoing embodiment does not involve the addition ormodification of signal lines between the GPS module 110 and the displaymodule 160, or the connection of additional measuring apparatus. Forthis reason, work is simplified for design optimization as well as noiseanalysis and countermeasures testing, and thus design, fabrication, andtesting processes can proceed more efficiently.

Moreover, since the secondary signal is simply ignored if the hostmodule of the electronic device does not support the reception ofsecondary signals, compatibility is preserved with existing electronicdevices.

The configuration of the GPS module 110 and display module 160 inaccordance with the embodiment described above is not only beneficialfor the manufacturers of respective modules or electronic devices, butalso for the users of such electronic devices. By using car navigationequipment implementing this configuration of the GPS module 110 anddisplay module 160, the user is able to determine the optimalinstallation position of the antenna or main unit of the equipment whileviewing the on-screen information.

3. Description of Modification

The above-described configuration in accordance with an embodiment ofthe present invention is applicable not only to noise observation, butalso to testing the antenna or the frequency converter in the GPSmodule. FIG. 15 is a schematic diagram illustrating an exemplaryconfiguration of a system for testing an antenna or frequency converterin a GPS module by applying the configuration of the GPS module 110 anddisplay module 160 in accordance with the embodiment described in theforegoing.

FIG. 15 shows the antenna 102, signal line 104, GPS module 110, anddisplay module 160 in accordance with the embodiment shown by way ofexample in FIG. 7. Additionally, a test antenna 202 is placed at aposition facing the antenna 102, and a signal generator 210 is connectedto the test antenna 202.

The signal generator 210 causes a test signal to be generated and outputto the test antenna 202. The test signal may be, for example, acontinuous wave (CW) on the GPS carrier frequency 1575.42 MHz at apredetermined level, such as −110 dBm. Once generated, the test signalis transmitted from the test antenna 202 to the antenna 102.Subsequently, the signal received by the antenna 102 isfrequency-converted in the frequency converter 120 of the GPS module110, and the frequency spectrum or statistical data for the resulting IFsignal is displayed on the screen of the display module 160. In sodoing, the performance of the frequency converter 120 in the GPS module110 can be tested on the basis of, for example, the ratio between the CWlevel in the frequency spectrum versus the level of the other frequencycomponents. Furthermore, the antenna 102 can also be tested by replacingthe antenna 102 connected to the GPS module 110 during observation.

The foregoing thus describes a preferred embodiment of the presentinvention in detail and with reference to the attached drawings.However, it should be appreciated that the present invention is notlimited to such an example. It is obvious to those skilled in the artthat various modifications and substitutions may be made withoutdeparting from the scope of the technical ideas disclosed in theattached claims, and that any such modifications or substitutions areunderstood to be naturally included in the technical scope of thepresent invention.

By way of example, the present specification primarily describes signalprocessing related to global navigation satellite systems (GNSS) such asGPS. However, an embodiment of the present invention described above isalso applicable to general spread spectrum wireless systems.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-089218 filedin the Japan Patent Office on Apr. 1, 2009, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A signal processing apparatus, comprising: a synchronizer configuredto acquire synchronization with the spreading code of an intermediatefrequency signal that is obtained by converting the frequency of areceived signal into a predetermined intermediate frequency, wherein thereceived signal is received from a satellite in a global positioningsystem; a demodulator configured to demodulate a message contained inthe intermediate frequency signal synchronized by the synchronizer; ameasuring unit configured to output a primary signal to a predeterminedsignal line, wherein the primary signal expresses the results ofmeasuring at least one from among the position, velocity, and time ofthe apparatus as measured on the basis of the message that wasdemodulated by the demodulator; and a secondary signal output unitconfigured to attach a predetermined header to a secondary signal andoutput the result to the predetermined signal line, wherein thesecondary signal contains at least the intermediate frequency signal, ora signal generated from the intermediate frequency signal.
 2. The signalprocessing apparatus according to claim 1, wherein the secondary signalcontains a signal expressing a frequency spectrum generated by applyinga Fourier transform to the intermediate frequency signal.
 3. The signalprocessing apparatus according to claim 1 or 2, wherein the secondarysignal contains a signal expressing data obtained by statisticallyanalyzing a frequency spectrum generated as a result of applying aFourier transform to the intermediate frequency signal.
 4. The signalprocessing apparatus according to claim 1, further comprising: afrequency converter configured to generate the intermediate frequencysignal by converting the frequency of a received signal into apredetermined intermediate frequency, wherein the received signal isreceived from a satellite in a global positioning system.
 5. The signalprocessing apparatus according to claim 1, wherein the secondary signaloutput unit is configured to attach to the secondary signal a headerthat contains an ID code for identifying the type of signal included inthe secondary signal.
 6. An information processing apparatus,comprising: a primary signal acquirer configured to acquire a primarysignal from a predetermined signal line, wherein the primary signalexpresses at least one from among the position, velocity, and time ofthe apparatus as measured on the basis of an intermediate frequencysignal obtained by converting the frequency of a received signal into anintermediate frequency, and wherein the received signal is received froma satellite in a global positioning system; a secondary signal acquirerconfigured to acquire a secondary signal from the predetermined signalline, wherein the secondary signal contains at least the intermediatefrequency signal, or a signal generated from the intermediate frequencysignal; and a display unit able to display, on a given screen, datacorresponding to the primary signal acquired by the primary signalacquirer, as well as data corresponding to the secondary signal acquiredby the secondary signal acquirer.
 7. The information processingapparatus according to claim 6, wherein the secondary signal containsthe intermediate frequency signal, the apparatus further comprising: adata processor configured to generate a frequency spectrum by applying aFourier transform to the intermediate frequency signal; and wherein thedisplay unit displays on-screen the frequency spectrum generated by thedata processor.
 8. The information processing apparatus according toclaim 6, wherein the secondary signal contains a signal expressing afrequency spectrum generated by applying a Fourier transform to theintermediate frequency signal, the apparatus further comprising: a dataprocessor configured to statistically analyze the frequency spectrumcontained in the secondary signal; and wherein the display unit displayson-screen the data obtained as a result of the analysis by the dataprocessor.
 9. The information processing apparatus according to claim 6,wherein the secondary signal acquirer acquires the secondary signal fromamong the signals output to the predetermined signal line by acquiringthe signal whose attached header contains the ID code corresponding tothe secondary signal.
 10. A signal processing method, comprising thesteps of: acquiring synchronization with the spreading code of anintermediate frequency signal that is obtained by converting thefrequency of a received signal into a predetermined intermediatefrequency, wherein the received signal is received from a satellite in aglobal positioning system; demodulating a message contained in thesynchronized intermediate frequency signal; outputting a primary signalto a predetermined signal line, wherein the primary signal expreses theresults of measuring at least one from among the position, velocity, andtime of the apparatus as measured on the basis of the demodulatedmessage; and attaching a predetermined header to a secondary signal andoutputting the result to the predetermined signal line, wherein thesecondary signal contains at least the intermediate frequency signal, ora signal generated from the intermediate frequency signal.
 11. A programfor causing a computer that controls a signal processing apparatus tofunction as: a synchronizer configured to acquire synchronization withthe spreading code of an intermediate frequency signal that is obtainedby converting the frequency of a received signal into a predeterminedintermediate frequency, wherein the received signal is received from asatellite in a global positioning system; a demodulator configured todemodulate a message contained in the intermediate frequency signalsynchronized by the synchronizer; a measuring unit configured to outputa primary signal to a predetermined signal line, wherein the primarysignal expresses the results of measuring at least one from among theposition, velocity, and time of the apparatus as measured on the basisof the message that was demodulated by the demodulator; and a secondarysignal output unit configured to attach a predetermined header to asecondary signal and output the result to the predetermined signal line,wherein the secondary signal contains at least the intermediatefrequency signal, or a signal generated from the intermediate frequencysignal.
 12. A data display method executed using an informationprocessing apparatus able to display data on a given screen, the methodcomprising the steps of: acquiring a primary signal from a predeterminedsignal line, wherein the primary signal expresses at least one fromamong the position, velocity, and time of the apparatus as measured onthe basis of an intermediate frequency signal obtained by converting thefrequency of a received signal into an intermediate frequency, andwherein the received signal is received from a satellite in a globalpositioning system; acquiring a secondary signal from the predeterminedsignal line, wherein the secondary signal contains at least theintermediate frequency signal, or a signal generated from theintermediate frequency signal; and displaying, on the given screen, datacorresponding to the primary signal, as well as data corresponding tothe secondary signal.
 13. A program executed by a computer that controlsan information processing apparatus able to display data on a givenscreen, the program causing the computer to function as: a primarysignal acquirer configured to acquire a primary signal from apredetermined signal line, wherein the primary signal expresses at leastone from among the position, velocity, and time of the apparatus asmeasured on the basis of an intermediate frequency signal obtained byconverting the frequency of a received signal into an intermediatefrequency, and wherein the received signal is received from a satellitein a global positioning system; a secondary signal acquirer configuredto acquire a secondary signal from the predetermined signal line,wherein the secondary signal contains at least the intermediatefrequency signal, or a signal generated from the intermediate frequencysignal; and a display unit able to display, on the given screen, datacorresponding to the primary signal acquired by the primary signalacquirer, as well as data corresponding to the secondary signal acquiredby the secondary signal acquirer.